Sudden Excessive Blow By

[hrtull]

I removed head, removed Number 3 piston that had 160 psi. I was hoping to find a very obvious problem but found nothing. Head gasket was perfect, head appears fine, oil and coolant clean. Piston , rings and sleeve appear to be same as other 2 cylinders. Valve ,rocker, lifters seem fine. Nothing stands out as a problem and in my opinion those are the worst type of problem.
There is something that I might have overlooked from the beginning. Last November when I did first repair and replaced all the rings there was an O ring included with each set. I assumed they were for another application/another model because I never found mention of them being used in this tractor a YM186 engine 3T72HA and I never attempted to install them. Also there were no O rings on first sleeve removal. I assumed the head gasket makes the sleeve to block seal. Here is a picture of the sleeve with groove, then with the O ring and a pic comparing O ring size to sleeve. To be clear O rings were never installed, this just shows how they could be installed if required. Dont know for sure if these were the O rings that were included with ring set, but the only 3 matching O rings I had as I never throw O rings away. Dont know and hoping someone can advise on O ring. Maybe this number 3 piston/sleeve is just worn more and low pressure. Thanks for any suggestions. HT

[winston]

Everything I read indicates a dry sleeve and no o-ring.

You are saying an o-ring was included in each ring set. I don't understand that?? I would sure be interested to know what the o-rings are for.

Have you checked ring end gap?

Having a hard time wrapping my head around this happening all of a sudden with blow by and yet no evidence of a problem. You did use a new head gasket? Asking because Heidegeist2000 had mentioned you cleaned the cylinder gasket and I am not sure what gasket he is referring too.

Did you go by the attachment showing sleeve installation measurements on page one?

[hrtull]

Winston thanks for your reply. I found the problem . The piston groove/flange was cracked per the picture. I should have removed rings first thing to inspect. I studied that piston several times but when I remove the rings it revealed itself. I am glad knowing what the problem is but now concerned why this is the second busted piston. I can accept the first original one breaking , it came with the tractor when I purchased it with no history or known maintenance. Is the second one breaking just bad luck, coincidental or bad install on my part. I know this piston was good when I installed new rings. I had no issue compressing rings and installing piston into sleeve. The ring clearance/gap was .012 and within tolerance. I am debating with myself if I should replace the middle piston which is currently at 300psi. This would make all pistons new instead new ones on each end and old one in middle. In a nutshell, Purchased tractor, did restoration and used for about 20 hrs with no issues. Then front piston broke. Replaced that piston and added new rings to all 3 pistons . Used tractor for less that an hour after repair and all seemed well in late November. Now in February with only a few hours this second piston Brakes. Also I did use new head gasket , satisfied O rings not used. Do you have any clues what is happening with pistons cracking. Dont know if injectors could be causing an issue. Going to try and get them tested. Also do you do private emails and if so how is that done on forum. Anyway, Thanks again, HT

[Aaron]

even the 300psi cylinders are quite a bit below that engine's lower limit.

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An injector that 'squirts' instead of misting the fuel can cause unburned liquid fuel to collect in the combustion area (fuel flooding I think it is called) and would certainly put a lot of stress on the piston grooves. I think low compression could also cause the fuel to collect & hammer like that.
https://mzwmotor.com/piston-damage-symptoms

I think we need to figure out why all of the cylinders have such low compression.

You are certain the valves were set correctly?